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Biogas is a fuel generated from organic waste such as animal dung, agricultural waste and household waste. The gas is produced during the anaerobic decomposition of these waste materials and its most useful component is methane (60%). The gas can be used for cooking and lighting and also in conventional vehicles. The gas can also be burned in a generator to make electricity.

It is easy to recover gas from the reactor and more energy is generated by biogas digestion than by combustion. Biogas plants also only need a part-time operator as they rely on micro-organisms to digest the waste matter. The other main by-product of biogas production is slurry which can then be dried and used as a soil conditioner. The use of cow dung and straw to produce biogas for domestic cooking has been successfully proven and over 1200 families have replaced their firewood stoves with such biogas units in Sri Lanka.
   The Process

The anaerobic digestion process which is the basic process giving rise to biogas can serve the people in many ways – in fact it is a technology with triple benefits and no real disadvantages: environmental protection, energy & power generation and soil conditioner production

The process of anaerobic digestion consists of three steps.

1. Decomposition (hydrolysis or plant of animal matter. This step breaks down the organic material to usable-sized molecules such as sugar).

2. Conversion of decomposed matter to organic acids.

3. Conversion of acids to methane gas.
   Biogas Technologies

There are two types of biogas reactors in use in Sri Lanka, the Dry Batch System and the Continuous System. The widely used Continuous System needs to be fed on a daily basis so these are usually positioned next to cattle sheds to ensure an uninterrupted supply of dung. However this type of reactor can only be used in a limited number of areas as cattle in the dry zone generally roam and farmers therefore do not have large cattle sheds. The alternative system is a locally developed digester type named the Sri Lankan Dry Batch System. This system principally uses straw which is widely available in the paddy cultivating dry zone areas of Sri Lanka. Biogas technology which can produce energy and electricity as well as organic fertilizer therefore has the potential to become an integral part of agricultural society.
   Socioeconomic Benefits of Biogas Power

• Freely available matter such as cow dung or straw is used to produce biogas which can then be piped into the home for cooking, lighting and other purposes

• Fuel wood is traditionally used for cooking in Sri Lanka and the replacement of this with biogas saves women a lot of time as there is no longer a need to collect wood for cooking tasks. This frees up time for the women to pursue other activities to generate additional income

• Compost produced as a by-product can be used to fertilise vegetables which can then be sold as organic produce

• Fuel wood and fertiliser costs are steadily increasing in Sri Lanka so biogas generation saves household expenditure

   Environmental Benefits of Biogas Power

• Biogas plants effectively process organic waste materials, improving the surrounding environment for communities and reducing disposal costs

• Biogas plants can be used in the treatment of industrial wastes

• The by-product of biogas generation plants can be used as an ideal soil conditioner.
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